Powdery detergents have been widely applied to domestic use. Powdery detergents are highly flowable, hardly cake, form little dust, are easy to handle and are highly soluble. Most of these detergents are produced through spray drying.
Recently, the demand for high-density detergent granules has increased, since these detergents conserve resources. Furthermore, high-density detergents are handy to carry, which makes them convenient for consumers.
However detergent granules produced by spray drying generally have an apparent specific gravity of 0.4 g/cm.sup.3 or less and an average particle size of 200 to 1000 .mu.m. Therefore it is difficult to directly produce high-density detergent granules by a conventional spray drying method.
Typical methods for the production of high-density detergent granules as described above include those disclosed in JP-A-61-69897 and JP-A-61-76597, JP-B-58-44120 and JP-A-61-76598. (The term "JP-A" as used herein means a "published unexamined Japanese patent application" and the term "JP-B" as used herein means a "published examined Japanese patent publication").
Namely, known methods for the production of high-density detergent granules comprise granulating spray-dried detergent particles, as disclosed in JP-A-61-69897; mixing detergent components, solidifying the mixture and grinding the same to thereby obtain detergent granules, as disclosed in JP-A-61-76597; or granulating a high-density detergent by using a turntable, as disclosed in JP-B-58-44120 and JP-A-61-76598.
JP-A-61-69897 discloses a batchwise method for the production of highly flowable high-density detergent granules which comprises mixing components in a vertical reaction tank having stirring blades attached to a vertical axis. In this method, however, additional batch reactors are required to accommodate an increase in production capacity.
JP-A-61-76597 discloses a method for the production of a high-density detergent powder which comprises mixing detergent components in a kneader, solidifying the mixture and then grinding the same. However this method is disadvantageous in that the moisture content of the starting materials is limited such that the grinding operation consumes a large amount of electrical power.
Furthermore, JP-B-58-44120 discloses the use of a turntable having a rough surface. In this case, however, a large amount of detergent granules adhere to the rough surface of the turntable. Furthermore, JP-A-61-76598 discloses a method wherein a smooth turntable is used to reduce the amount of detergent granules adhering to the turntable. However this method is still disadvantageous in that a sufficient rotational power required for the granulation of the detergent granules cannot be obtained since detergent granules slip on the surface of the turntable, such that the rotary speed of the turntable must be increased. As a result, the detergent granules are subjected to high temperatures for a prolonged period of time.